Vol. 60.] LATER FORMATIONS SURROUNDING THE DARDANELLES. 261 



there are, I believe, some small fragments remaining about a mile 

 south of Keshan, at Karakaya Dere, where the Oligocene sand- 

 stones are overlain by a thin series of soft limestones, in which I 

 have found Prosodacna, Dreissensia, and Neritina. At Hafus Hassan 

 Tchiflik, 3 miles west of Keshan, Prosodacna, Anodonta, Planorbis, 

 and Melania occur in shelly sand. Near Boz Tepe, 6 miles west of 

 Keshan, Jlelanojjsis Martiniana occurs ; and near Tekekeui, 3 miles 

 south of Keshan, I have obtained Lyrccea Bonelli from sandy 

 beds overlying the Oligocene sandstones. 



At Myriophyto, Bithynia and Melania were found in soft clay 

 taken out of a shallow well. 



VII. Pliocene. 



Prof. Andrussov has come to the conclusion that the Pontus 

 existed as a large, perhaps also deep, brackish lake, enclosed on 

 all sides, from the Pontian until the beginning of the Diluvial 

 Epoch (26, p. 73), and that the Bosphorus is the bottom of a 

 fluvial valley lowered beneath the sea-level (24, xxix, p. 9). 



The details of several facts bearing on this question, which I have 

 observed, may now be given to confirm this view ; and I would call 

 special attention to the post- Sarmatic eastward extension of 

 the central fold of Tertiary rocks, resulting in the upheaval 

 of the Dohan-Aslan and Serian-Tepe ridge. This upheaval closed 

 the connection between the Marmora basin and the Gulf of Xeros 

 (PI. XXII, fig. 2) by the formation of a dam which, though much 

 weathered down, is still 180 feet above the present water-level. 



This upheaval, moreover, has led to the exposure of some of the 

 older rocks near the axis of folding. Epidote-quartz-rock, calcite 

 or dolomite, and chlorite, with calcareous tuffs and andesite, appear 

 at Dohan Asian, while a large expanse of foliated and sheared 

 serpentine, with calcite, dolomite, and hornblende-schist extends, 

 in an east-north-easterly direction, from Bournar Oren through 

 Serian Tepe to Yolzdik. That this ridge is post-Sarmatic is proved 

 beyond question by the steep inclination away from it, on either 

 side, with a continuous east-north-easterly strike, of the Tertiary 

 sedimentaries, up to and including the Sarmatic. 



The dam thus formed, confining the Marmora water from any 

 outlet to the westward, was the proximate cause of the cutting of 

 the Bosphorus, and of the drainage of the Marmora into the Black 

 Sea, during Pliocene times. Later on, as will be shown, it similarly 

 resulted in the cutting of the Dardanelles and the drainage of the 

 combined Black-Sea and Marmora water into the Mediterranean. 



Since no traces of Tertiary deposits have been found as yet alono- 

 the Bosphorus, to my knowledge, it is useless to speculate as to 

 how or when the valley, which now forms the channel, first took a 

 connected shape in the old rocks. To all appearance it was developed 

 on the recession of the Sarmatic sea, as that of a river running to 

 the north-eastward, and confined within a narrow rocky gor°-e 



